Plant protection - overseas and in Australia

Diquat and conservation tillage

The development suited ICI Australia well because of the dominant importance of Australia's agriculture and its great potential for improved productivity. Manufacture of several compounds of this family was commenced in Australia in the mid-forties, not only by ICI Australia but also by Monsanto, Timbrol and, later, by a West Australian entrepreneur, a former employee of ICI Australia. In spite of ICI's strong patent position in the UK, ICI did not dominate the development overseas, particularly opposite American Chemical (AmChem) in the USA, since wartime legislation had prevented ICI from filing patents of strategic value overseas.

In the late fifties ICI UK made another key invention in this field or -more correctly, two -paraquat ('Gramoxone') and diquat ('Reglone'). These compounds, very similar in structure and collectively referred to as bipyridyls, are broad spectrum herbicides with the remarkable property that they act on weeds within thirty minutes, hence are rain-fast, yet are rapidly inactivated on contact with the soil. Their potential was clearly immense, provided they could be made cheaply enough. Pyridine, however, a heterocyclic compound, was not particularly cheap and its condensation to the appropriate bypyridyls was difficult. One, paraquat, could only be made by a process involving sodium (highly reactive with moisture) and complex plant and safety engineering; for the other, diquat, according to reports of the time 'no industrial process was in sight'. As ICI Australia's chemists had access to ICI's reports and unpublished patent applications they were aware of the target. Just then they (the late K. H. Pausaecker and G. Varcoe) noted a publication by two South Australian scientists, Badger and Sasse,[92] describing the catalytic dehydrogenation of pyridine over Raney nickel yielding o-bipyridyl, an important intermediate for diquat. They verified the work but found that the reaction quickly died off with very low yields. Catalyst poisoning was suspected but removal of all impurities did not remedy the problem. Varcoe[93] solved the problem by elegant chemical engineering, by continuous displacement of the reaction products after minimal contact with recycled pyridine vapour and liquid; the concept -at the same time -provided the basis for design of the full scale plant. ICI UK colleagues, working on the project with a much larger team, had to agree that their Australian friends had solved the problem of an industrial scale synthesis, but the Australians' understandable euphoria was soon dampened when they did their costs. A plant was economic only on the basis of the much larger European market and its much cheaper raw materials. A great deal more R&D was done in the UK on the bipyridyls over the years -some 30 million dollars worth[94] -and a plant for the European markets and some exports was built. The bipyridyls were established as one of the world's great biologicals and the ICI Australia process is still in operation.

Australian Academy of Technological Sciences and Engineering